mirror of https://github.com/docker/cli.git
166 lines
6.4 KiB
Markdown
166 lines
6.4 KiB
Markdown
# attach
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<!---MARKER_GEN_START-->
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Attach local standard input, output, and error streams to a running container
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### Aliases
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`docker container attach`, `docker attach`
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### Options
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| Name | Type | Default | Description |
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|:--------------------------------|:---------|:--------|:----------------------------------------------------|
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| [`--detach-keys`](#detach-keys) | `string` | | Override the key sequence for detaching a container |
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| `--no-stdin` | `bool` | | Do not attach STDIN |
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| `--sig-proxy` | `bool` | `true` | Proxy all received signals to the process |
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<!---MARKER_GEN_END-->
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## Description
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Use `docker attach` to attach your terminal's standard input, output, and error
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(or any combination of the three) to a running container using the container's
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ID or name. This lets you view its output or control it interactively, as
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though the commands were running directly in your terminal.
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> [!NOTE]
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> The `attach` command displays the output of the container's `ENTRYPOINT` and
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> `CMD` process. This can appear as if the attach command is hung when in fact
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> the process may simply not be writing any output at that time.
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You can attach to the same contained process multiple times simultaneously,
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from different sessions on the Docker host.
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To stop a container, use `CTRL-c`. This key sequence sends `SIGKILL` to the
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container. If `--sig-proxy` is true (the default),`CTRL-c` sends a `SIGINT` to
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the container. If the container was run with `-i` and `-t`, you can detach from
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a container and leave it running using the `CTRL-p CTRL-q` key sequence.
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> [!NOTE]
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> A process running as PID 1 inside a container is treated specially by
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> Linux: it ignores any signal with the default action. So, the process
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> doesn't terminate on `SIGINT` or `SIGTERM` unless it's coded to do so.
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You can't redirect the standard input of a `docker attach` command while
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attaching to a TTY-enabled container (using the `-i` and `-t` options).
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While a client is connected to container's `stdio` using `docker attach`,
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Docker uses a ~1MB memory buffer to maximize the throughput of the application.
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Once this buffer is full, the speed of the API connection is affected, and so
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this impacts the output process' writing speed. This is similar to other
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applications like SSH. Because of this, it isn't recommended to run
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performance-critical applications that generate a lot of output in the
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foreground over a slow client connection. Instead, use the `docker logs`
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command to get access to the logs.
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## Examples
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### Attach to and detach from a running container
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The following example starts an Alpine container running `top` in detached mode,
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then attaches to the container;
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```console
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$ docker run -d --name topdemo alpine top -b
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$ docker attach topdemo
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Mem: 2395856K used, 5638884K free, 2328K shrd, 61904K buff, 1524264K cached
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CPU: 0% usr 0% sys 0% nic 99% idle 0% io 0% irq 0% sirq
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Load average: 0.15 0.06 0.01 1/567 6
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PID PPID USER STAT VSZ %VSZ CPU %CPU COMMAND
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1 0 root R 1700 0% 3 0% top -b
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```
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As the container was started without the `-i`, and `-t` options, signals are
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forwarded to the attached process, which means that the default `CTRL-p CTRL-q`
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detach key sequence produces no effect, but pressing `CTRL-c` terminates the
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container:
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```console
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<...>
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PID PPID USER STAT VSZ %VSZ CPU %CPU COMMAND
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1 0 root R 1700 0% 7 0% top -b
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^P^Q
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^C
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$ docker ps -a --filter name=topdemo
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CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
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96254a235bd6 alpine "top -b" 44 seconds ago Exited (130) 8 seconds ago topdemo
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```
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Repeating the example above, but this time with the `-i` and `-t` options set;
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```console
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$ docker run -dit --name topdemo2 alpine /usr/bin/top -b
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```
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Now, when attaching to the container, and pressing the `CTRL-p CTRL-q` ("read
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escape sequence"), the Docker CLI is handling the detach sequence, and the
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`attach` command is detached from the container. Checking the container's status
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with `docker ps` shows that the container is still running in the background:
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```console
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$ docker attach topdemo2
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Mem: 2405344K used, 5629396K free, 2512K shrd, 65100K buff, 1524952K cached
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CPU: 0% usr 0% sys 0% nic 99% idle 0% io 0% irq 0% sirq
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Load average: 0.12 0.12 0.05 1/594 6
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PID PPID USER STAT VSZ %VSZ CPU %CPU COMMAND
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1 0 root R 1700 0% 3 0% top -b
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read escape sequence
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$ docker ps -a --filter name=topdemo2
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CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
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fde88b83c2c2 alpine "top -b" 22 seconds ago Up 21 seconds topdemo2
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```
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### Get the exit code of the container's command
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And in this second example, you can see the exit code returned by the `bash`
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process is returned by the `docker attach` command to its caller too:
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```console
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$ docker run --name test -dit alpine
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275c44472aebd77c926d4527885bb09f2f6db21d878c75f0a1c212c03d3bcfab
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$ docker attach test
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/# exit 13
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$ echo $?
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13
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$ docker ps -a --filter name=test
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CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
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a2fe3fd886db alpine "/bin/sh" About a minute ago Exited (13) 40 seconds ago test
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```
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### <a name="detach-keys"></a> Override the detach sequence (--detach-keys)
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Use the `--detach-keys` option to override the Docker key sequence for detach.
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This is useful if the Docker default sequence conflicts with key sequence you
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use for other applications. There are two ways to define your own detach key
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sequence, as a per-container override or as a configuration property on your
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entire configuration.
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To override the sequence for an individual container, use the
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`--detach-keys="<sequence>"` flag with the `docker attach` command. The format of
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the `<sequence>` is either a letter [a-Z], or the `ctrl-` combined with any of
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the following:
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* `a-z` (a single lowercase alpha character )
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* `@` (at sign)
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* `[` (left bracket)
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* `\\` (two backward slashes)
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* `_` (underscore)
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* `^` (caret)
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These `a`, `ctrl-a`, `X`, or `ctrl-\\` values are all examples of valid key
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sequences. To configure a different configuration default key sequence for all
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containers, see [**Configuration file** section](https://docs.docker.com/reference/cli/docker/#configuration-files).
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